assertions

nimony/lib/std/assertions.nim

• const assertionsEnabled: bool

  Whether assert expands to anything at all. Follows Nim's convention: -d:release KEEPS assertions, -d:danger removes them, and -d:noAssertions removes them on its own — the last one so a build can drop the checks without also turning off bound checks and overflow checks, which is what you want when profiling: an assert costs a compare, a branch and a string literal at every call site, and those are not what is being measured.

• proc raiseAssert(msg: string)
• template assert(cond: bool; msg: string)
• template assertRc(r: ref T not nil; expected: int64; tag: string)

  Diagnostic for ref-count tracking. r is a ref T, internally a pointer to {rc: int, d: T} (see arc.nim); reads the rc field at offset 0 and aborts when it differs from expected. arcDec returns true when rc goes negative, so a fresh ref has rc=0 (= 1 logical reference); each =dup adds +1, each =destroy adds -1. Use assertRc(myRef, 0) after construction or assertRc(myRef, n) after n duplications to catch over- or under-counting before the symptom (UAF, double-free, leak) drifts far from the cause.

• template assertRcAlive(r: ref T not nil; tag: string)

  Looser assertRc: only fail when rc has already gone negative (i.e. the block has been freed and we're walking dangling memory). Useful when the exact rc varies with =dup/=destroy interleaving but you still want to catch use-after-free quickly. Also rejects bogus pointers (large absolute rc) since arcDec'd-into-positive-billions still indicates the block was reused for an unrelated allocation.